Zeolite beta is a crystalline aluminosilicate molecular sieve zeolite which finds application in a number of industrial processes including as a catalyst in various hydrocarbon conversion reactions such as hydrocracking, hydroisomerization and dewaxing. Zeolite beta, like many other molecular sieve zeolites, is synthesized by the hydrothermal digestion of a reaction mixture comprising silica, alumina, an alkali alkaline earth metal and an organic templating agent. The organic agent acts as a template in the nucleation and growth of the zeolite beta crystals. Once the crystals are formed, it is conventional practice to carry out a calcination treatment in order to remove the organic material from the interstitial channels of the molecular sieve network.
Crystalline zeolite beta, which is identified by its x-ray defraction pattern, and basic procedures for its preparation are disclosed in U.S. Pat. No. 3,308,069 to Wadlinger et al. The chemical composition of zeolite beta in the as synthesized form as disclosed in the patent to Wadlinger et al. may be characterized as follows: EQU [X m/2 (1.0 1-x) TEA] AlO.sub.2 .multidot.yS.sub.i O.sub.2 .multidot.WH.sub.2 O
Wherein:
X is less than 1, PA1 m is at least one cation, usually an alkali metal or alkaline earth metal, more specifically sodium, PA1 n is the valance of M, Y is from about 5 to 100, PA1 W is about 4, and PA1 TEA represents the tetraethylammonium ion. PA1 SiO.sub.2 /Al.sub.2 O.sub.3 --from about 10 to about 200 PA1 Na.sub.2 O/tetraethylammonium hydroxide (TEAOH).sup.- from about 0-0.1 PA1 TEAOH/SiO.sub.2.sup.- from about 0.1-1.0 PA1 H.sub.2 O/TEAOH.sup.- from about 20 to about 75
As described in Wadlinger et al., zeolite beta may be formed from a mixture in water of tetraethylammonium hydroxide and suitable sources of sodium monoxide (or hydroxide), alumina, and silica. Typical reaction mixture compositions, in terms of mole ratios, fall within the following ranges:
The resulting reaction mixture can be heated at a temperature of about 75.degree. to about 200.degree. C. until crystallization of the molecular sieve zeolite occurs. The crystallized product can be separated from the reaction mixture by filtration or centrifuging and then washed with water and dried to remove water from the molecular sieve network. The product can then be calcined in air or in an inert atmosphere in order to remove the templating agent as described above.
The Wadlinger patent discloses that the catalytic materials can be prepared by calcining the original sodium form of the zeolite beta and/or replacing the major portion of the sodium ions with other metallic or ammoniacal ions. Specifically disclosed in Wadlinger (Example 2) is a composition containing after calcination in air at 55.degree. C., 0.7 mole percent Na.sub.2 O. Disclosed in Example 8 is a product formed by treating a dried product which was exchanged continuously for 48 hours with 2% solution of ammonium chloride. After washing free of excess chloride ions, the catalyst was dried and calcined for 3 hours at 1000.degree. F. to produce an acid beta aluminosilicate having 0.07% Na content.
Various other procedures are known for the synthesis of zeolite beta. For example, European Patent Application 159,846 to Rubin discloses the synthesis of zeolite beta having a silica/alumina mole ratio of up to 300 employing a templating agent formed by the combination of dimethylbenzylamine and benzyl halide. The hydrothermal digestion procedure in which the crystals are formed is carried out at a temperature below 175.degree. C. in order to avoid the formation of undesirable side effects. The zeolite beta, produced in accordance with the Rubin application, when employed either as an absorbent or a catalyst, can be at least partially dehydrated by heating at a temperature of about 200.degree.-600.degree. C. in an air or nitrogen atmosphere for about 1-48 hours. The inorganic cations of freshly synthesized zeolite beta can be decomposed by heating to a temperature up to about 550.degree. C. for 1-48 hours. Zeolite beta prepared in accordance with the Rubin process can have the original cations associated therewith replaced by a wide variety of other cations including hydrogen, ammonium and metal cations and mixtures thereof.
European Patent Application 165,208 by Bruce et al. discloses a procedure for the preparation of zeolite beta, similar to that disclosed in the aforementioned Rubin application except that the templating agent is a dibenzyl dimethyl ammonium halide or hydroxide with the silica/alumina components employed to provide a silica/alumina mole ratio in the synthesized product of about 20-250.
U.S. Pat. No. 4,642,226 to Calvert et al. discloses a process for the preparation of zeolite beta which is similar to those disclosed in the aforementioned European patent applications and which employs dibenzil dimethylammonium hydroxide or chloride as a templating agent. The reaction mixture in Calvert is heated at a temperature of about 80.degree. to about 175.degree. C. for about 1 to about 120 days. The Calvert patent states that the zeolite beta can be used in either in the organic nitrogen-containing an alkali metal containing form, the alkali metal form and hydrogen form or another univalent or multivalent cationic form. Calvert also discloses that zeolite beta can be used in intimate combination with a metallic component, e.g., a hydrogenation component such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese or a noble metal such as platinum or palladium. The patent further states that the zeolite beta should be at least partially dehydrated when employed either as an absorbent or as a catalyst or as a hydrocarbon conversion catalyst. Chlorides, nitrates and sulfates are disclosed as ion exchange agents. Calvert et al. discloses zeolite beta of relatively low sodium contents, e.g., 0.14 wt. % Na and 0.11 wt. % Na.
In another process for the preparation of zeolite beta, is disclosed European Patent Application 164939 to Calvert. The synthesis procedures disclosed here are similar to those in the above-mentioned references, except that a tetraethylammonium bromide or hydroxide templating agent is employed to produce a partially crystalline product of extremely high silica/alumina ratio which is said to be less expensive than fully crystalline zeolite beta which is dealuminized to provide a corresponding silica/alumina mole ratio. The digestion period in this procedure is for a period of about 1-7 days at a temperature of 90.degree.-200.degree. C. The silica/alumina ratio of the zeolite beta produced here ranges from 20-1000 and is preferably greater than 200.
European Application 186,447 by Kennedy et al. discloses the use of zeolite beta in catalytic cracking processes. The zeolite beta may be used in the as synthesized form following calcination of and be of either low or high silica/alumina activities. It may be synthesized with trivalent framework ions other than aluminum to form, for example, borosilicates, boroaluminosilicates, gallosilicates, or galloaluminosilicates structural isotypes, which are considered to constitute forms of zeolite beta. The zeolite beta may be acid extracted to form the high silica/alumina products.
As noted previously, the Wadlinger et al. and Calvert et al. patents disclose zeolite beta of relatively low sodium content, although they attribute no particular advantage to this characteristic. The use of certain zeolites of moderate but not extremely low sodium content as molecular sieve catalysts in hydrocarbon conversion processes is known in the art. U.S. Pat. No. 4,185,040 to Ward et al. discloses an alkylation process employing a zeolite catalyst of low sodium content which is said to be especially useful in the production of ethylbenzene from benzene and ethylene and cumene from benzene and propylene. The Na.sub.2 O content should be less than 0.7 wt. % and preferably less than 0.5 wt. %. Examples of suitable zeolites include molecular sieves of the X, Y, L, B, ZSM-5, and omega crystal types with steam stabilized hydrogen Y zeolite being preferred. Specifically disclosed is a steam stabilized ammonium Y zeolite containing about 0.2 Na.sub.2 O.
Another alkylation procedure is disclosed in European Patent Application 272,830 to Ratcliffe et al. Ratcliffe procedure involves the use of alkylation catalysts which have been treated in a manner to improve selectivity to monoalkylation in an aromatic alkylation procedure, specifically the propylation of benzene to produce cumene. The selectivity of the molecular sieve containing alkylation catalyst is said to be increased by at least one percentage point by first depositing a carbonaceous material on the catalyst and then subjecting the resultant carbon containing catalyst particles to combustion. Specifically disclosed zeolitic crystalline molecular sieves include those selected from the group of Y zeolites, fluorided Y zeolites, X zeolites, zeolite beta, zeolite L and zeolite omega. The zeolites may be modified products of reduced alumina content and reduced sodium content. A preferred zeolite is Y zeolite produced by first ammonium exchanging to produce an ammonium exchanged zeolite of a sodium content of about 0.6 wt. %, expressed as Na.sub.2 O, calcining at a temperature of about 315.degree.-900.degree. C. in the presence of steam, and then ammonium exchanging the steamed calcined zeolite to obtain a product having less than 1.0 wt. % and preferably less than about 0.2 wt. % sodium expressed as Na.sub.2 O.